1. Field of the Disclosure
The present invention relates to, for example, a power supply device that can be appropriately used to charge a terminal provided with a wireless communication function, such as a mobile telephone terminal device, a communication terminal device charged through the use of power transmitted from the power supply device, and a non-contact power transmission method used for the power supply device.
In recent years, power has been transmitted from a device such as a charger to a different terminal device in a non-contact state where a power supply end or the like is not connected to the different terminal device to charge a secondary battery provided in the different terminal device.
An electromagnetic induction scheme has been available as a non-contact power transfer scheme of related art. According to the electromagnetic induction scheme, a power transmission coil is provided in the power transmission-side device and a power reception coil is provided in the power reception-side terminal device. Then, the part where the power transmission coil of the power transmission-side device is provided is brought near to that where the power reception coil of the power reception-side device is provided to produce the magnetic flux coupling between the power transmission coil and the power reception coil so that the power transmission is attained in a non-contact manner.
For example, a power transmission coil 11 is provided in a terminal device 10a and a power reception coil 12 is provided in a terminal device 10b as illustrated in FIG. 8. Then, the power transmission coil 11 of the terminal device 10a is brought near to the power reception coil 12 of the terminal device 10b as illustrated in FIG. 8 so that power is transmitted from the power transmission coil 11 to the power reception coil 12.
The terminal device 10b provided on the power reception-side can use the transmitted power to charge a secondary battery provided in the terminal device 10b. Otherwise, the terminal device 10b can use the transmitted power as operation power thereof.
The electromagnetic induction scheme is a non-contact power transfer technology that has been widely used. However, under the electromagnetic induction scheme, power can be transferred over a distance of the order of few millimeters so that power can be transferred between devices that are significantly close to each other. At present, therefore, the electromagnetic induction scheme has been used for some devices including, for example, a waterproof terminal with a charging end that can be exposed with difficulty.
On the other hand, in recent years, a so-called magnetic resonance scheme has been developed and put to practical use as a scheme for efficiently transmitting power to a terminal device provided at some distance in a non-contact manner. Namely, an LC circuit including a coil, a capacitor, and so forth is provided in each of the power transmission-side device and the power reception-side device to establish the electric field-and-magnetic field resonance between both the LC circuits so that the wireless power transfer is achieved. Frequencies that are used to establish the electric field-and-magnetic field resonance between both the LC circuits should be equivalent to each other.
Under the magnetic resonance scheme, the near-field power transfer can be performed over a distance of the order of few centimeters to few meters. Further, when a plurality of the power reception-side devices is provided in a power transferable range, power can be transferred from a single power transmission-side device to the power reception-side devices at one time.
For example, three terminal devices 20a, 20b, and 20c are provided in the neighborhood of one another as illustrated in FIG. 9. The terminal device 20a includes a magnetic resonance-power transmission coil 21 and each of the terminal devices 20b and 20c includes a magnetic resonance-power reception coil 22. The two terminal devices 20b and 20c are provided in a power transfer range Ap defined for the terminal device 20a. 
When the resonance frequencies of the three terminal devices 20a, 20b, and 20c are equivalent to one another in that state, power can be transferred from the single terminal device 20a to the two terminal devices 20b and 20c at one time. However, compared to the power transmitted to the single terminal device, the power transmitted to each of the terminal devices 20b and 20c is reduced by half or around so long as the configuration of the terminal device 20b is equivalent to that of the terminal device 20c. 
Japanese Unexamined Patent Application Publication No. 2006-353042 discloses the following technology. Namely, for charging a terminal device in a non-contact manner, the terminal device is identified through near-field communications or the like, and the identified terminal device is charged.